Valuable? Hastings 1066 FDC?

Have just posted a link to a UK FDC from 1966 with one stamp from the series of Battle of Hastings stamps.
The FDC in itself is of little value, but the fact that the original letter is inside and was sent to a child telling that this FDC might be valuable one day adds to the value.

The letter inside the envelope often adds much value to a simple postal cover of FDC.

For me, it would depend on who wrote the letter and, or, to whom it was addressed. If either or both were well-known individuals I would consider it an association cover and would consider buying it, if not over priced. If both are unknown, an accompanying letter urging the recipient to keep the cover is not that big of a deal and I'd pass regardless of price.

Don

PS:

I saw the cover and letter below after writing the above. As 50 + years have proved, the future value the aunt mentioned was wishful thinking. Enclosures like the one here are not all that common in contemporary FDCs, but neither do they add much value when found. Regrettably, I think the cover will be a hard sell.